An environmentally-friendly technology of a vehicle is a core technology that controls a survival of a future automobile industry and advanced car makers have focused their own energy on the development of an environmentally-friendly vehicle to achieve environment and fuel efficiency regulations.
Therefore, the car makers have developed an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV) as a future vehicle technology.
The car makers have focused on future vehicles as an alternative plan of practical problems for satisfying exhaust gas regulations and improving fuel efficiency and have steadily conducted research and development to put the future vehicles to practical use.
Generally, the electric vehicle, the hybrid electric vehicle, and the plug-in hybrid electric vehicle are driven by a driving motor that obtains a torque with electric energy.
In particular, the hybrid electric vehicle is a vehicle using at least two power sources. As the power source of the hybrid electric vehicle, an engine and a driving motor have been used. The hybrid electric vehicle not only uses an optimum operation region of the engine and the driving motor but also recovers energy at the time of braking, thereby improving fuel efficiency and efficiently using energy.
The hybrid electric vehicle uses a voltage of a main battery (high voltage battery) to drive the driving motor and uses a voltage of an auxiliary battery (low voltage battery) to drive an electric load. The electric load includes electric and electronic apparatuses using the voltage of the auxiliary battery, such as a head lamp, an air conditioner, and a wiper. To convert the high voltage supplied from the main battery into a low voltage and supply the low voltage to the electric load as an operating voltage, a low voltage DC-DC converter (LDC) is disposed between the main battery and the auxiliary battery.
FIG. 6 is a graph showing charging efficiency of an auxiliary battery.
As illustrated in FIG. 6, if a state of charge (SOC) of the auxiliary battery reaches a predetermined SOC, the charging efficiency of the auxiliary battery is suddenly decreased. The predetermined SOC is changed according to specifications of the auxiliary battery and is approximately 70% to 80%. When the auxiliary battery is charged in a section in which the charging efficiency of the auxiliary battery is suddenly decreased, a lot of energy loss is caused. To minimize the energy loss, it may be considered to prohibit the auxiliary battery from being charged in the section. However, when the charged amount of the auxiliary battery is too small, the auxiliary battery may be discharged while a vehicle stops and the auxiliary battery is recharged by the energy of the main battery, and therefore a maximum drivable distance of the vehicle may be decreased.
Therefore, a method for changing an SOC capable of charging an auxiliary battery as much as possible in consideration of a driving cycle of a driver is required.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.